He received the go ahead 90 minutes before kickoff, and there were no signs of pain.
It took every big play he and Jay Cutler could muster down the stretch to rally the Chicago Bears back from 17 points down and stun the Niners 28-20 on Sunday night to spoil their home debut at new Levi's Stadium.
Cutler threw two of his three touchdown passes to Marshall in the fourth quarter and also connected with Martellus Bennett for the go-ahead score for his second TD pass in a 27-second span.
''I just tried to stay positive and speak positive things into existence,'' Marshall said. ''I knew once I got to the game if I could at least jog, Adrenalin would kick in and I would be able to run a little bit.''
Run, leap and stretch out. That's what Marshall did on a 17-yard touchdown catch late in the first half that put his team on the board and proved key in the Bears (1-1) bouncing back from a 23-20 Week 1 home loss in overtime to the Bills.
Here are some things to know from the Bears' comeback win over San Francisco (1-1):
MOMENTUM SWITCH: Chicago coach Marc Trestman credits Cutler for setting the example throughout a tough week in the wake of a 23-20 overtime loss to the Bills in the season opener.
The skeptics questioned the Bears, and Cutler stayed the course.
''We all looked to him this week to see how he responded,'' Trestman said.
WARD'S LESSON: Rookie defensive back and 49ers' first-round draft pick Jimmie Ward got beat on all three of Marshall's touchdowns. Outsized and outdone.
The first was Marshall's 17-yard touchdown catch late in the first half in which he made a leaping, one-handed snag to pull the ball into his body as he fell into the end zone.
''I just threw my hand out there and it stuck,'' Marshall cracked.
Getting on the board before halftime gave the Bears a lift.
''The play he made really sparked us, that was an exceptional catch on any field at any time and I think that really sparked our football team,'' Trestman said. ''It was incredibly important to have something to hang our hats on.''
Harbaugh isn't singling out one player over another in why this one got away.
''Really, I feel like we all have fingerprints on this one, and we'll look and see exactly what we could have done differently or how we can improve from it. And I feel like we will be able to and we'll come back stronger for it.''
BANGED-UP BEARS: Last week, Chicago was down key playmakers on the offensive side. Now, the defense is reeling. The Bears still found a way with backup defenders making big plays when it mattered most.
''We step on the field every time with an edge,'' Fuller said. ''That helped us to pull this one out.''
MISTAKES APLENTY: A week after the 49ers forced four takeaways in a dominant season-opening victory at Dallas, San Francisco made all the mistakes. Kaepernick had the three interceptions and a lost fumble, and the Niners committed 16 penalties for 118 lost yards.
Kaepernick's 57.0 passer rating ranked as his third-lowest in his 25 career regular-season starts. He was 21 for 34 for 248 yards with four sacks and three interceptions.
''Terrible,'' said Kaepernick, who was flagged for unsportsmanlike conduct after Fuller's first pick for ''inappropriate language'' that the QB denied.
The mistakes cost San Francisco on a night it outgained Chicago 361-216.
San Francisco missed a chance to make an early statement in the NFC West on a day the defending Super Bowl champion Seattle Seahawks lost at San Diego.
''I'm not going to cry over it,'' Crabtree said. ''We gave this game away. We have to find the killer instinct.''
49ERS TIGHT ENDS: Vernon Davis, who caught two touchdown passes in a season-opening win at Dallas, hobbled through the disappointed locker room on crutches making sure to put no pressure on his injured left ankle.
San Francisco also lost tight end Vance McDonald to a knee injury as the 49ers lost a home opener for the first time under fourth-year coach Jim Harbaugh.
Harbaugh had no update on Davis' injury.
AP NFL websites: www.pro32.ap.org and www.twitter.com/AP-NFL